compile:
    [javac] Compiling 502 source files to /Users/marcus/src/jdk9/nashorn/build/classes
    [javac] warning: [options] bootstrap class path not set in conjunction with -source 1.8
    [javac] /Users/marcus/src/jdk9/nashorn/src/jdk.scripting.nashorn/share/classes/jdk/nashorn/internal/objects/NativeArrayBuffer.java:228: warning: [cast] redundant cast to ByteBuffer
    [javac] return (ByteBuffer)nb.duplicate().position(offset);
    [javac] ^
    [javac] /Users/marcus/src/jdk9/nashorn/src/jdk.scripting.nashorn/share/classes/jdk/nashorn/internal/objects/NativeArrayBuffer.java:232: warning: [cast] redundant cast to ByteBuffer
    [javac] return (ByteBuffer)getBuffer(offset).limit(length);
    [javac] ^
    [javac] /Users/marcus/src/jdk9/nashorn/src/jdk.scripting.nashorn/share/classes/jdk/nashorn/internal/objects/NativeFloat32Array.java:84: warning: [cast] redundant cast to FloatBuffer
    [javac] super(((FloatBuffer)nb.position(start).limit(end)).slice(), end - start);
    [javac] ^
    [javac] /Users/marcus/src/jdk9/nashorn/src/jdk.scripting.nashorn/share/classes/jdk/nashorn/internal/objects/NativeFloat64Array.java:84: warning: [cast] redundant cast to DoubleBuffer
    [javac] super(((DoubleBuffer)nb.position(start).limit(end)).slice(), end - start);
    [javac] ^
    [javac] /Users/marcus/src/jdk9/nashorn/src/jdk.scripting.nashorn/share/classes/jdk/nashorn/internal/objects/NativeInt16Array.java:85: warning: [cast] redundant cast to ShortBuffer
    [javac] super(((ShortBuffer)nb.position(start).limit(end)).slice(), end - start);
    [javac] ^
    [javac] /Users/marcus/src/jdk9/nashorn/src/jdk.scripting.nashorn/share/classes/jdk/nashorn/internal/objects/NativeInt32Array.java:84: warning: [cast] redundant cast to IntBuffer
    [javac] super(((IntBuffer)nb.position(start).limit(end)).slice(), end - start);
    [javac] ^
    [javac] /Users/marcus/src/jdk9/nashorn/src/jdk.scripting.nashorn/share/classes/jdk/nashorn/internal/objects/NativeInt8Array.java:83: warning: [cast] redundant cast to ByteBuffer
    [javac] super(((ByteBuffer)nb.position(start).limit(end)).slice(), end - start);
    [javac] ^
    [javac] /Users/marcus/src/jdk9/nashorn/src/jdk.scripting.nashorn/share/classes/jdk/nashorn/internal/objects/NativeUint16Array.java:84: warning: [cast] redundant cast to CharBuffer
    [javac] super(((CharBuffer)nb.position(start).limit(end)).slice(), end - start);
    [javac] ^
    [javac] /Users/marcus/src/jdk9/nashorn/src/jdk.scripting.nashorn/share/classes/jdk/nashorn/internal/objects/NativeUint32Array.java:85: warning: [cast] redundant cast to IntBuffer
    [javac] super(((IntBuffer)nb.position(start).limit(end)).slice(), end - start);
    [javac] ^
    [javac] /Users/marcus/src/jdk9/nashorn/src/jdk.scripting.nashorn/share/classes/jdk/nashorn/internal/objects/NativeUint8Array.java:84: warning: [cast] redundant cast to ByteBuffer
    [javac] super(((ByteBuffer)nb.position(start).limit(end)).slice(), end - start);
    [javac] ^
    [javac] /Users/marcus/src/jdk9/nashorn/src/jdk.scripting.nashorn/share/classes/jdk/nashorn/internal/objects/NativeUint8ClampedArray.java:88: warning: [cast] redundant cast to ByteBuffer
    [javac] super(((ByteBuffer)nb.position(start).limit(end)).slice(), end - start);
    [javac] ^
    [javac] 12 warnings
    [javac] Creating empty /Users/marcus/src/jdk9/nashorn/build/classes/jdk/nashorn/internal/objects/package-info.class
    [javac] Creating empty /Users/marcus/src/jdk9/nashorn/build/classes/jdk/nashorn/api/scripting/package-info.class
     [copy] Copying 1 file to /Users/marcus/src/jdk9/nashorn/build/classes/META-INF/services
     [copy] Copying 1 file to /Users/marcus/src/jdk9/nashorn/build/classes/jdk/nashorn/api/scripting/resources
     [copy] Copying 14 files to /Users/marcus/src/jdk9/nashorn/build/classes/jdk/nashorn/internal/runtime/resources
     [copy] Copying 2 files to /Users/marcus/src/jdk9/nashorn/build/classes/jdk/nashorn/tools/resources
     [copy] Copying 1 file to /Users/marcus/src/jdk9/nashorn/build/classes/jdk/internal/dynalink/support
     [copy] Copying 1 fil


This is correct- the casts shouldn't need to be there.
The problem is that if I remove them, I break backwards compatibility towards earlier 9 builds than b38, and compatibility with 8.

I can easily remove these redundant casts and push to 9, but I need to know if breaking backwards compatibility to builds < b38 is acceptable. This would make it hard for us to, e.g., build and regression test against earlier builds.

Advice needed.